Regulation system in the manufacture of hot rolled strips by means of a multi-stand hot rolling mill

ABSTRACT

The invention relates to control in the manufacture of hot strip by means of a multi-stand hot-strip rolling mill, especially a wide-strip rolling mill, which has a higher-order process control system with a sampling plan with the initial and final dimensions, with material data, rolling temperatures, etc., and a guidance system for setpoint control of lower-order decoupled individual regulators for the variable functional parameters of the individual roll stands, e.g. roll adjustment, rotational speed, torque, etc., with the setpoints of the individual regulators being determined by means of a computation process using model equations with convergent parameter adjustment to the actual parameters, in such fashion that a working point control that can be determined in advance is provided and section control and regulation are accomplished by changing the load distribution on the individual stands in such fashion that the working points lie in the previously determined tolerance range of a shape control line.

BACKGROUND OF THE INVENTION

The present invention relates to a controller for controlling themanufacturing of hot strip using a multi-stand hot-strip rolling mill,and, in particular, a wide-strip mill. A sampling plan including initialand final measurements, material data, rolling temperatures, etc. isprovided. A control system for controlling the setpoint of lower-ordercoupled individual controllers for the variable functional parameters ofthe individual stands (e.g. roll adjustment, rotational speed, torque,etc.) is also provided. In the present invention the setpoints of theindividual controllers are computed using model equations involvingconvergent parameter adjustment to the actual parameters such thatsetpoint control, that can be predetermined, is obtained.

In hot-strip rolling mills, producing a strip having a required sectiondevelopment and flatness by means of a small number of simple rollingmill stands, without requiring costly mechanical roll actuators isdesired. If the need for roll actuators is unavoidable, these actuatorsshould be simple and limited to only a few rolling mill stands.Particularly, in hot wide-strip mill trains designed according to thesecriteria, there was formerly no way to optimize the thickness section ofthe strip. A sampling plan design based on experiential values continuesto be the norm.

The European Patent Application EP-0 121 148 B1 discusses a section andflatness control for hot-strip tandem mill trains in which the stripsection at the critical thickness (below which no significant reshapingof the rolled strip can be achieved) is used as the basis of anexpensive flatness and section development control of the hot strip. Anequivalent control is disclosed in the German Patent Application DE-2736 234 A2. Rolling mill trains with the above mentioned controls requirea plurality of thickness, section, and flatness measuring devices alongthe mill train and expensive stand controls. As a result, the total costof a hot strip whose production is controlled in this fashion is high.This is especially true when a wide strip rolling train is used.Further, both the measured values and the roll actuators are costly tomaintain and significantly increase operating expenses.

The goal of the present invention is to provide a control forcontrolling the manufacturing of hot strip with a multiple-standhot-strip rolling mill, and in particular, a wide-strip mill. Thecontrol of the present invention permits the mill to produce rolledstrip within tolerance by employing model calculations, especially withthe aid of automatically adaptable model calculations. Hence, thecontrol of the present invention requires only a minimum of expense. Inparticular, old rolling mill trains can be modernized with the controlaccording to the present invention without having to rebuild the rollingmill trains and without needing to provide the rolling mill trains witha plurality of expensive measuring devices and actuators on the rollstands.

SUMMARY OF THE INVENTION

The present invention realizes the above mentioned goal by providingsection control and regulation that uses changes in the loaddistribution on the individual stands such that their working points liewithin a "shape funnel" defined by the predetermined tolerance range ofa section control line. Using a computation technique in which therolling mill engineer has considerable confidence because of long yearsof experience, it is possible to achieve the required section andflatness values with simple rolling mill technology, primarily only byinfluencing the principal influential parameter in the rolling process,i.e., the distribution of the required total roll separating force overthe individual stands. The present invention achieves the correct loaddistribution by using a shape control line for the required adaptationmodel. Together with other measures which cooperate with the primarycontrol measure of suitable load distribution, the required section isobtained for strips with different rolling temperatures, sectiondesigns, final thicknesses, etc. Thus, the regulating and calculatingtechnique according to the present invention can significantly reducethe "hardware" expense in rolling technology while simultaneouslyincreasing flexibility.

The design of the present invention provides that the tolerance range ofthe shape control lines, which is surprisingly present and can beutilized, is smaller (deviation angle β) below the critical thickness(below which a relative section constancy is obtained) and is larger(deviation angle α) above the critical thickness. Thus, the physicalconditions on a rolling mill train can be advantageously used to achieveregulation and computation optimization and not merely positioning on aline determined in advance.

In another embodiment of the present invention, a "shape funnel" definedby the tolerance range of the shape control lines, with transitions forthe limits of β and α is obtained in the area of the critical thickness.In this embodiment, the shape funnel is made symmetrical to the shapecontrol lines below the critical thickness and asymmetrical above thecritical thickness in the area of the deviation angle, especially in aratio of 2:1, between the area above and below the shape control lines.Thus an optimization range adjusted for the physical realities in therolling mill for the load distribution calculation in which the shapecontrol line can be pivoted or changed in another way is simplyobtained. Within the shape funnel, the optimization computer rapidlycalculates the load distribution possibilities for rolling and can shedsome light on the question of whether, and at what load distribution,the required section can be reached at a specified thickness or whetherthe specified thickness or section cannot be obtained in this way for aparticular rolling mill train. When the calculation of the optimizationcomputer indicates that the specified section or specified thicknesscannot be achieved, boundary conditions may have to be changed oradditional actuators must be provided and installed for the roll stands.Influencing the section and the final thickness using roll actuators areknown to the rolling mill engineer.

To calculate the shape control lines, the data from the specifiedsection of the strip produced are used. When the calculation yieldsworking points outside the shape flannel, a recalculation takes placewith new load distribution assumptions until all the working points liein the shape funnel. When the optimization calculation indicates that inaddition to changing the load distribution on the individual stands,additional factors must act on the rolling process to maintain thetolerance range of the shape control lines, this is advantageouslyaccomplished by influencing the roll re-deflection, the roll shift,and/or roll transposition, and/or by influencing the thermal convexity,possibly by cooling or even by hydraulic or thermal influence. A changein the roll microsection can also result as a consequence of theoptimization calculation in conjunction with the shape funnel. It isadvantageous in this regard constantly to compensate for the factorsthat influence roll wear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a rolling mill train showing theregulating structure and the most important individual parameters.

FIG. 2 is a schematic representation of the work rolls of a rolling millstand.

FIG. 3 illustrates shape control lines and their tolerance range.

DETAILED DESCRIPTION

In FIG. 1, reference 1 refers to the rolls of the individual stands of arolling mill train, 2 represents the rolled strip, and 3 represents themeasuring devices and sensors for the individual rolls 1 and theirdrives as well for other function blocks, e.g. for the nip, etc. Theregulators and positioning devices for the rolls are designated 3a.

The measured values of the measuring devices and sensors 3 are adjustedat 4 after which they pass to statistical measured value protectiondevice 5. Using these values, the sampling plan is recalculated at 6 andthe algorithms used for the sampling plan recalculation are adapted at7. The values from 7 are transferred in 9 to the sampling plancalculation which determines, among other things, the roll separatingforce, rolling torque, especially the section, but also the adjustment.The sampling plan calculation includes the data from the rollingstrategy summarized at 8, which is formulated, in particular, from thetype of material, finished thickness, and specified section as well asadditional operator and computer data. The sampling plan calculation 9provides the setpoint selection values calculated in 10 and fed to theindividual regulators and positioning devices 3a for the individualworking point regulators.

The function blocks shown in FIG. 1 are advantageously combined in acomputer. However it is also possible to perform such processing inseparate computers or in separate pans of one computer. Suitablecomputers in which the computations for the individual regulators can beperformed are known. Their programming as well as a parameterization ofthe individual regulators is based on operating handbooks of such knowncomputers.

In FIG. 2, reference 11 refers to a lower work roll, 12 to an upper workroll, and 13 to the rolled strip. The schematic representation does notaccount for the roll deflection produced by the influence of the rollseparating force opposed to the strip shape shown, but indicates thetheoretical convex shape (camber) of the work rolls. The strip has edgethicknesses D_(RR) and D_(RL) and a thickness D_(M) at the center. Theedge thickness, for example (C₄₀) is measured at the strip edge used.The section value P for the calculation is obtained from therelationship P =D_(M) -(D_(RR) +D_(RL))/2 and is normally expressed inmicrons. The respective special section development follows therequirements of the downstream cold rolling mill train or therequirements for the hot strip produced.

In FIG. 3, reference 14 refers to the shape control line with lowertolerance limit 15 and upper tolerance limit 16. At points 17 and 18,which lie in the area of critical thickness, below which the materialflow in the transverse direction can only occur within very narrowlimits, the pitch of limiting curves 15 and 16 changes. The limitingcurves 15 and 16 define a "shape funnel" which has the symmetrictolerance limit angle β below the critical thickness. Above the criticalthickness has the tolerance limiting angle α upward from the spacecontrol line 14 and α/2 downward from the shape control line 14. Thissimplified definition of the "shape funnel" is especially favorable fromthe computational standpoint and is sufficiently accurate as well.

As may be seen, shape control line 14 runs through the zero point whenextended. The working points may be adjusted so long as they remainwithin tolerance limit curves 15 and 16. The specified section and finalthickness are specified by shape control line 14. The influence of theroll separating force is the main factor affecting random reduction.Other influential parameters involved in rolling technology on the otherhand become less important and constitute only auxiliary parameters.Redistribution of the roll separating force therefore constitutes theessential factor for the section and thickness that are obtained. Thebasic condition is the maintenance of the total roll separating force,i.e., the total reduction required.

Below the critical thickness, the strip section obtained acts directlyon the flatness of the strip during subsequent processing, so that ittoo is predetermined by the thickness of the strip and the strip sectionwith only minor opportunities for influence.

We claim:
 1. In a multi-stand, hot-strip, rolling mill for manufacturinga hot strip having a critical thickness below which material flow in adirection transverse to a roll can only occur within very narrow limits,the rolling millincluding a plurality of individual roll stands, each ofthe roll stands being regulated by regulators, and having parametersmeasured by measuring devices, including a sample plan determinationdevice being provided with initial and final dimensions, with materialdata, and with rolling temperatures, and adapted to determine a samplingplan for controlling the regulators, and including a processor whichuses model equations with convergent parameter adjustment to actualparameters being used to determine setpoints of the regulators,a processfor predefining a working point control, comprising steps of: a)predefining a shape control line as a function of a final thickness ofthe hot strip at a specified section; b) predefining a tolerance rangefor said shape control line, wherein said predefined tolerance range isnarrower below the critical thickness than above the critical thickness;c) adopting a working point control if all working points defining theworking point control lie within the predefined tolerance range; and d)changing load distribution at the plurality of individual roll stands ifat least one of the working points lies outside of the predefinedtolerance range.
 2. The process of claim 1 wherein said predefinedtolerance range is defined by a deviation angle alpha above the criticalthickness and a deviation angle beta below the critical thickness, alphabeing greater than beta.
 3. The process of claim 2 wherein the deviationangles alpha and beta define a shape funnel having a throat at thecritical thickness.
 4. The process of claim 3 wherein the shape funnelis symmetrical to the shape control line in an area below the criticalthickness and asymmetrical to the shape control line in an area abovethe critical thickness.
 5. The process of claim 4 wherein the deviationangle alpha defined by an upper limit of the tolerance range above theshape control line is approximately twice a deviation angle defined by alower limit of the tolerance range below the shape control line.
 6. Theprocess of claim 1 further comprising a step of calculating the shapecontrol line with data of a final section of a hot strip desired to beproduced.
 7. The process of claim 6 further comprising a step ofrecalculating the data of the final section if working points lieoutside the tolerance range.
 8. The process of claim 1 furthercomprising a step of exerting an influence on roll re-deflection if atleast one of the working points lies outside of the predefined tolerancerange.
 9. The process of claim 1 further comprising a step of exertingan influence on at least one of a group consisting of roll displacementand roll transposition if at least one of the working points liesoutside of the predefined tolerance range.
 10. The process of claim 1further comprising a step of changing a roll microsection if at leastone of the working points lies outside of the predefined tolerancerange.
 11. The process of claim 1 further comprising a step ofinfluencing a thermal change in convexity if at least one of the workingpoints lies outside of the predefined tolerance range.
 12. The processof claim 1 further comprising a step of redistributing a roll separatingforce of the individual stands based on ideal shape control lines. 13.The process of claim 1 further comprising a step of calculating adistribution of individual roll separating forces in a shape funnelbased on a shape control line in an optimizing computer to achieve atotal roll separation force required for a rolling mill train.